1. Field of the Invention
The present invention is directed to a method and apparatus for applying laser beam energy in the treatment of medical conditions. Specifically, the present invention is directed to a method and apparatus for applying low-level laser beam energy, using a vertical cavity surface-emitting laser or an array thereof, to promote angiogenesis of the heart muscle wall following cardiac ischemia, during and after myocardial revascularization, and immediately following acute myocardial infarction and for a time thereafter. Additionally, the present invention is directed to a method and apparatus for applying low power laser therapy directly to the coronary vasculature and blood system affected by these medical conditions.
2. Background
The number one killer in the U.S. and worldwide is heart disease accounting for 1,500,000 heart attacks in the U.S. and 500,000 U.S. deaths per year. As a result of coronary artery disease ("CAD"), individuals suffer from insufficient blood supply to the heart muscle. This can result in silent cardiac ischemia in which the patient is unaware that there is a deficiency of blood supply to the heart muscle. Another form of CAD manifests itself in chest pains--angina pectoris--and the disease in either of these forms can progress to myocardial infarct or acute complete deficiency of blood supply to the heart muscle.
When the disease progresses to this stage ("MI") there is pennanent damage to the heart muscle starting with deterioration of the heart muscle due to weakening of the collagen framework and progressing to expansion of the heart wall. If healing does not occur in time, the heart wall ruptures and death occurs.
The present methods of treatment involves drugs to thin the blood, drugs to reduce high blood pressure, balloon angioplasty and stents to expand the narrowed coronary arteries, thrombolytic drugs to open the blocked arteries in acute MI, and a number of invasive surgical procedures with their attendant mortality risks. After spending approximately $300 million on drug research in the past ten years no effective drug therapy has been discovered and the death rate from MI continues to remain at about 500,000/year in the U.S. and is bound to grow with the increase in the average age of the population.
The application of laser beam energy in the treatment of medical conditions such as wounds, ulcers, nerve injuries and muscle injuries is known. Studies have shown that low-power laser beam energy (1-500 mW) and in varying wavelengths (400-1300 nm) delivering 0.5-7 J/cm.sup.2 is effective in the treatment of these various medical conditions.
Studies have shown that low power laser energy stimulates fibroblasts and other cells important in the wound healing process to release a number of growth factors in greater amounts than without laser photostimulation, thus enhancing and accelerating the wound healing process. Increased proliferation of fibroblasts and keratinocytes has been reported in a number of studies as well as the release of cytokines from Langerhans cells and the release of growth factors from macrophages.
Wei Yu reported in Photochemistry and Photobiology, 1994 that low energy laser irradiation increased the release of basic fibroblast growth factor (bfGF). bfGF is a potent mitogen and chemoattractant for fibroblasts and endothelial cells and induces a predominantly angiogenic response in the healing wound. These growth factors stimulate growth of new blood vessels in the healing wound ("angiogenesis"), increased collagen deposition, and increased tensile strength in the healing scar.
Of importance to this particular application, low power laser therapy has been shown to enhance and accelerate wound healing and reduce scar tissue while enhancing the collagen composition and tensile strength of the healed scar. Enwemeka reported this effect in healing rabbit tendons in Laser Therapy Journal--1994. A significant clinical demonstration of the increased tensile strength of scars healed with low power laser therapy was reported recently by Kleinman et al. in Laser Therapy Journal--1996.
The ability to influence and accelerate the formation of collagen and microcirculation immediately after MI by photomodulation is important in preventing the weakening of the collagen framework and subsequent expansion and rupture of the heart muscle which leads to death.
Low-level laser energy has also been known to have a profound effect on blood biochemical indexes, homeostasis, erythrocyte and leukocyte blood count, and platelet aggregation. In a study by Salansky published in The American Society of Laser Medicine and Surgery, transcutaneous application of 660 nm laser energy at 6 mW was shown to have a significant effect on leukocytes and erythrocytes. In that same study, photon irradiation resulted in significant activation of antioxidant enzymes, reduction of hyper-coagulation, and increase of lipid peroxidation in stress-immobilized animals.
In the Laser Therapy Journal, Kipshidze published a study of 900 patients with acute MI whose intravenous blood was irradiated with low-power laser energy within the first four hours following MI. Data of organ-specific enzyme monitoring and ECG mapping showed limitation of the ischemic area. Moreover, antioxidant blood activity and blood and tissue oxygen contents increased. ECG monitoring showed that laser therapy had a high antiarrhythmic effect and reduced ventricular fibrillation. Intravenous laser irradiation was shown to significantly limit the ischemic damage and accelerate the scarring process.
Conventional low power laser therapeutic devices generally comprise a hand-held probe with a single laser beam source, or a large, stationary table console with attached probe(s) powered by a conventional fixed power supply. A common laser beam source is a laser diode. Laser diodes are commercially available in varying power and wavelength combinations. Large probes which contain multiple laser diodes affixed to a stand are also known. Such large, multi-beam devices are typically very expensive and require extensive involvement of medical personnel when treating a patient.
For example, in a device such as the large probe containing multiple beam sources discussed above, this device is typically affixed to a stand which has to be focused and controlled by a doctor or ancillary medical personnel. In addition to adding to the cost of the device and the treatment therewith, such a device requires a patient to travel to the location of the laser treatment device in order to obtain the laser therapy. Studies have shown that such treatment typically must be provided on a regular basis (e.g., every few hours or daily) once the treatment is initiated in order to be effective and to produce optimum results. This requires numerous patient visits to the treatment facility or extensive waiting on the part of the patient. As it is common for problems to arise which necessitate a patient missing a visit to the treatment facility, or for a patient to be inconsistent in the times at which appointments are scheduled, the efficiency of the treatment regimen may be lowered or the length of the treatment regimen (i.e., the number of patient visits) may be increased.
In the case of emergency medical conditions, such as MI, a conventional hand-held device is a less than optimal solution. More specifically, the operator of the device would be required to continuously apply the apply the laser energy when needed. This would result in added labor costs, thus making the device even more expensive. Further, self-application of laser energy is not feasible.
In addition to increasing the financial cost to the patient, a patient may be adversely affected by the number of required visits to the treatment facility in ways which are less tangible. That is, in addition to being away from family members, a patient is generally incapable of working or otherwise being productive while at the treatment facility. The high number of visits interferes with a patient's normal routine and can adversely affect a patient's job performance or home life.
Accordingly, a need exists for a method and apparatus for low-power laser treatment of MI, that is economical, convenient and more efficient than was previously possible.